Several types of gradation spaces to be used for interpolation processing have been proposed to be adopted in conjunction with processing for interpolating an image captured through color filters disposed so as to achieve a specific color array such as the Bayer array, with the color components thereof sub-sampled and thus restoring the image to a color image. Patent reference literature 1 discloses a technology whereby after taking a simple average of the G color component with a linear gradation, each of the color components, i.e., the R color, the G color and the B color is converted to each of the color components in a logarithmic gradation space and then interpolated in color difference planes by taking the differences between the R color component and the G color component and between the B color component and the G color component in this gradation space. Patent reference literature 2 discloses a technology whereby the color component signals are converted in advance to signals in a gamma space (Ri/Γ, Gi/Γ, Bi/Γ) with Γ set equal to 2.4 in accordance with the processing executed after the interpolation processing e.g., compression processing, display processing and the like, and the extent of the quantization error attributable to the repeated execution of gradation conversion is minimized through integrated execution of image processing including the interpolation processing in the gamma space. Patent reference literature 3 discloses a technology whereby the color component signals are converted in a gamma space with square root characteristics and a clearly defined image is obtained by minimizing the adverse effect of shot noise contained in the image through interpolation processing executed in the gamma space.    Patent reference literature 1: U.S. Pat. No. 4,642,678    Patent reference literature 2: U.S. Pat. No. 5,172,227    Patent reference literature 3: Japanese Laid Open Patent Publication No. 2004-7164